Solving Sound problem with AGC

[Chris Barcellos]

Originally Posted by Guy McLoughlin

Hi Chris,

Personally, I would stick with sending the tone track to one channel, and then removing the tone track when editing. Unless you can be asolutely sure of removing the tone frequency completely from the finished audio ( say with a narrow band filter ), I would be concerned about it effecting things somewhere down the road.

Yes, that is my conclusion too.. we have an ENG 44 mixer that will mix multiple mics.

As far as separate sound we will go that route, but I would like to feed that camera at same time, and this method will work for that, especially recording to one track, with tone segregated out. Thanks for the input.

And I have now gotten it to the point that in a single shooter no crew hand held situation, I mount a Sennheiser mic on my camera rig, and feed it through my Beachtek, and can get some decent sound.

[Jay Morrissette]

Originally Posted by Chris Barcellos

As far as separate sound we will go that route, but I would like to feed that camera at same time, and this method will work for that, especially recording to one track, with tone segregated out. Thanks for the input.

And I have now gotten it to the point that in a single shooter no crew hand held situation, I mount a Sennheiser mic on my camera rig, and feed it through my Beachtek, and can get some decent sound.

I have not tried this, but I would imagine that you could use a Zoom H4N to record stereo ambient with the built in mics + boom & Lapel on its XLR inputs.

Then possibly attaching the headphone out to the 5D input.

If you want to use the pilot tone in addition to an external recording you might be able to use the H4N in multitrack mode to play the pilot tone while recording.

~Jay

[Dan Chung]

I'd be interested if the Zoom can downmix an XLR input and a built in mic on one channel, while leaving the other channel as just XLR. Then we could play the high frequency tone into that XLR leaving one good channel for boom or radio mic and still getting some nice ambient. Is this possible?

Also you would need to pad the zoom's line or headphone output as the 5dmkII only takes mic level.

Dan

[Bob Thompson]

Ipod touch and iphone have a free app "Dog Whistle" and this has a variable tone output, maybe this could be incorporated as the tone generator

[Guy McLoughlin]

Originally Posted by Jay Morrissette

I have not tried this, but I would imagine that you could use a Zoom H4N to record stereo ambient with the built in mics + boom & Lapel on its XLR inputs.

...A word of caution. I haven't worked with the new H4N yet, but I owned the Zoom H4 for about a year. It was a pretty good recorder, but the XLR pre-amps were garbage. I ended up buying a Sound Devices MixPre to feed a clean signal to the Zoom H4.

I would hope that Zoom has learned from their past mistakes, though I've read one review of the H4N that stated that the mic pre-amps are still pretty noisy.

This is the reason why I got rid of the Zoom H4 and switched to the Sony PCM-D50, which has far better audio capabilities. ( i.e. Much better built-in mics, much much quieter recordings, and will last 10+ hours on one set of batteries, where the Zoom H4 could barely last 2 hours )

[Jay Morrissette]

I decided to do a quick test to see just how noisy the H4N's pres are.

In my quick test they are very noisy. In a real world scenario I don't know how bad the signal to noise ratio would be.

My test was quick and simple:
I used a Beta 57 mic because that's what I had handy, and also because it isn't especially sensitive. I held the mic a foot away from my mouth and spoke in normal to soft voice. I had the rec level set to 80 out 100. The hiss was high enough to be distracting.

For comparison I plugged the same mic into a Mackie mixer which has VLZpro preamps, and set the gain to where I thought it should be, and sent the direct out into 1/4" input on the Zoom. With the record level at 11 out of 100 there was no preamp noise that I could hear, and my voice was significantly louder.

I can post the two clips somewhere if you would like to hear them.

I may try the same test using a Sony Lav that I have to see if preamp noise is an issue with that mic.

I guess at $350 for a 4 track recorder, you get what you pay for.

~Jay

[Guy McLoughlin]

Hmmm... Interesting review with sound samples of the Zoom H4n digital recorder

Brad Linder's blog: Zoom H4n audio take 2 - second time not so charming

[Chris Barcellos]

I was recently asked to test the Juiced Link CX231 on my camera, and give some feed back. That was probably based on my posting here, but I also posted in another thread about my first experience, and this repeats some of that.

First, let me say that the CX231 does not promise to resolve the AGC levels issue on the 5D. What I can see happening is Hudson or others cracking the AGC control, giving us gain adjustment as needed on the camera. In the meantime, if I want to get best sound into camera-- as many will want to do, the CX231 is a valuable tool.

Shooting with my Sennheiser ME-66, directly to the Juiced link seemed quieter in terms of background noise than my Beachtek DX4-A. This makes perfect sense because the Juiced Link has powered preamps on board. In fact, I believe the sound is similar to running my mic through my ENG44 and into the 5D.

I ran my high frequency silent test tone trick (using an mp3 file generated tone from Audacity at 15400 hz) into one side of the CX231 through my IRiver 895 player, and of course the ME66 in the other side, as discussed in my original post on this thread. With the gain frozen, the mic input has is very clean and back ground noise is very low. Again, at first blush, it seem as clean as when I did a similar set up with the ENG44. This set up should work fine for shooting one man single mic operation, until we are given gain control on the 5D MKII. I wondered if mic levels couldn't get high enough, with gain disabled on the 5D, but I was actually able to distort with too high of input on the mic side in one set up, so I don't think that is an issue, and a range of adjustments can be chosen from.

As I had tried with the Beachtec, I did try setting both the IRiver input and the Mic input on center with the Pan switches, but that created a warbling effect and ticking noise that made that unusable, I did not have that happen on my Beachtek, so I suspect it has to do with preamps and issues with mixing two signals.

Monitoring is still an issue with this set up. What I want to be able to do at minimum, is split the output from the CX231, and sending signal unchanged to the Camera, while using the other side of the split to act as monitor. At the suggestiong of Robert Rozak from Juiced Link, I am going to try this product:

http://www.boostaroo.com/

I hope to be able to split of of the output from CX231 while avoiding interference with the camera input.

Hopefully, the HUDSON project, which has already succeeded in adding a meter, and disabling the AG, will also provide monitoring through the AV port, in the same way that Canon does with the HV20, but we will have to make do until then.

I will report back with more testing of the CX231 and this camera combo.

[Chris Barcellos]

I started out the night with the intention of doing a thorough on screen demonstration of the the tone generator/Juiced Link CX231 i had messed with last night. I pluged my little LCD4Video monitor so I could center myself in the picture. I started getting that whine I had experience in shooting the DVChallenge film earlier last month...

After some testing, it is clear that there is signal generating from the output cord that interferes with mic imput, and that is what I had experience the entire shoot, when we were hooked up to a monitor most of the time. And there doesn't seem to be a resolution.

Has anyone experienced similar issue? How about with HDMI out. Is it possible that complaint s about sound in this camera are related to that issue ?

[Jon Fairhurst]

Hi Chris, I just received my juicedLink today and tried it with the iPod. Even without an SD monitor, I heard some rogue noises. On the other hand, the juicedLink into the MicroTrackII looks to be as clean as - if not cleaner than - my Mackie VLZ-Pro mixer into an Audiophile 192 capture card. I need to calibrate things and do a proper A/B, but the initial results of the CX-231 into the MicroTrackII are very encouraging. Frankly, I got way too much crosstalk and harmonics from the iPod trick to be useful recording with the 5D at this point. Maybe when the gain can be properly controlled, the results will be better.

For now, I recommend double system all the way - as well as a clean preamp ahead of any low-cost recorders.

[Chris Barcellos]

Jon, I am not sure what your set up is, so its hard to comment. What tone level are you using, and how are you feeding through the system. What are you setting the gain switches to on the Juiced Link, for instance.

I will note that when I run the tone into the juiced link at too high a level, I get a repeating, noise on the tone track. I suspect it is the AGC being hit with such a high volume trying to adjust. I am going to try to demonstrate the issues and solutions in a video I will work on this weekend or next.

While I understand your preference for double system, there are many situations where there is just a shooter, and that is what I am concerned with. From my rudimentary testing I think the combo of the Juiced Link and the tone generator can get us a quality input. I see it as a matter of calibration to get it to acceptable levels.

[Jon Fairhurst]

Hi Chris,

I'm running the Shuttle headphone output straight into one of the 5D channels (not having a 1/8" to XLR combination of cables/adapters at hand)

I'd rather be able to record into the 5D directly as well for some situations, but my test results were not promising. We really need Tramm's firmware to turn down the 5D gain. I really had to smother the 5D input to get the gain to reduce acceptably.

Functionally, it's the same number of boxes right now. When I remove the MicroTrackII, I end up adding the iPod Shuttle to the system.

Also, I have no visual meters or headphone monitor with the 5D. The sound quality (at least with my rudimentary setup) was poor compared to with the MicroTrackII. Sure, we would avoid syncing in post, but the quality hit and lack of monitoring are too high a price right now. Even if I improve my pilot signal results, the monitoring problem is still an issue.

With Tramm's firmware, we have a shot at recording into the camera using the preamp, but the jury is still out regarding sound quality and being able to monitor with headphones and the LCD at the same time.

So, for now, I recommend a double system with the 5D for good quality audio and monitoring. My fingers are crossed that we will have a good in-camera solution available from Magic Lantern firmware.

[Chris Barcellos]

Okay I did some more testing tonight with the JuicedLink CX231, and I think I arrived at a combination of settings that works pretty well, at least for my purposes. Here is how I had the Juiced Link set up:

Mp3 Player into channel 1, set an line level. Gain set at High, trim at 11 oclock position. Volume setting on Mp3 was best at around 30, but good at 25 too.

Sennheisrer Me66 with K6 power source into channel 2, Gain at Medium, trim set to 1 oclock position.

Pan is set Right on Channel 1, Left on Channel 2.

I ran this test with a roomful of cranky and snippy girls. They were drafted and didn't like it. I wanted a variety of sound. Grandpa was a bit snippy as a result.

In Vegas, I selected left channel only, and then rendered an .wma for upload.

It is attached for your review.

For my purposes, I think I can control this set up pretty well, and repeat these results regularly, now that I have run enough test.

The Juiced Link should be even better once Hudson gets the level control and meters on board !

Check out the file attached

[Jon Fairhurst]

Originally Posted by Chris Barcellos

I ran this test with a roomful of cranky and snippy girls. They were drafted and didn't like it. I wanted a variety of sound. Grandpa was a bit snippy as a result.

Ahh. Family dynamics with snippy kids. I've been there!

Looking at the levels, your noise floor is at about -40dB or so, which is fairly high. You had good, hot levels with headroom though. And I didn't hear anything funny - just white noise.

It would be interesting to do a quick recording with the same level settings in a silent (yeah, right) environment. Maybe go into a closet or a car, put the mic on a stand (no handling noise), and point it into a box lined with foam or a towel or something. That would give us an idea of the noise floor.

Anyway, -40dB noise floor isn't all that great. I got closer to -70dB with the juicedLink, MicroTrackII and Rode NT1-A, and that was with a computer running in the background. My effective gain was lower though. I had my voice at about -18dB when a couple of feet from the mic. That said, The NT1-A isn't all that sensitive. I was running High gain at about twelve noon when I got -70dB. Your preamp settings were much lower (medium), so that tells me that the noise floor was set by the camera.

BTW, my camera tests had a similar noise floor to your file.

Hopefully, the Magic Lantern will be able to reduce the camera gain (and noise) further.

The 5D2 has a 16 bit A/D. That gives a dynamic range of 96dB (6dB per bit.) At 40dB, the camera is only delivering 7-bit audio(!) The -70dB noise floor is closer to 12-bits of dynamic range - and I recorded at 24 bits! It looks like 16-bit recording is all I need for this combination of mic, pre and recorder. No reason to use any more memory space than needed...

[Peer Landa]

Originally Posted by Jon Fairhurst

The 5D2 has a 16 bit A/D. That gives a dynamic range of 96dB (6dB per bit.)

Yes, theoretically 16 bit will give you 96dB, but in real life this will most likely be in the low 80s.

-- peer